Digital, electronic and other appliances, such as computer keyboards, tabletop telephones, cellular phones, smart phones, hand-held computers, tablet PCs, hand-held terminals, control systems of digital, electronic or electric instrumentation such as operation panels in airplanes, weapon activation systems, testing equipment and so on, are all equipped with pushbuttons (keys), keyboards, or touch screens.
The recent dramatic minimization of such systems and the physical constraints that sometimes exist, have led to a situation in which several different functions (i.e. the selection of a specific numeral or letter or symbol) are associated with a single key, since there are more functions than there are keys. One existing solution that enables a user to select a specific function associated with a specific key is the rapid, repeated pressing of the said key, whereby the desired function is selected by the number of times the user rapidly presses the key. For example, FIG. 1 depicts a schematic keyboard of a standard cellular phone that is in message writing mode. Pressing the “2” key once will select the letter “a”; pressing the “2” key twice in rapid succession will select the letter “b”; three consecutive presses will select the letter “c”; and the result of four consecutive presses will be the numeral “2”. This solution is cumbersome and inconvenient and any error in pressing the key (which is a very common occurrence) leads to the need to repeat the entire sequence so as to reach the desired function. Nevertheless, the currently existing knowledge in the said field has several drawbacks: First, it is still necessary to press the key several times in order to select the desired function (for instance, when a group of characters was associated with a specific key/finger during the initialization process). Second, the system's initialization process (i.e. the enrollment of the fingerprints and their association with specific, pre-defined keys, or characters, or groups of characters) is very cumbersome and is not user-friendly. In addition, this method (of associating/pre-defining a specific finger to a key and/or a character and/or a group of characters) requires the user to remember these pre-defined associations during the regular operation of the appliance (when he or she must sometimes work fast). In addition, some of the knowledge pertains to keys on appliances, as mentioned, that refer to four fingers of only one hand.